Staphylococcus aureus is a major cause of human diseases. The acquisition of broad antibiotic resistance in this bacterium, especially, methicillin and vancomycin-resistant S. aureus strains pose a major threat to public health. Various stress conditions within the host are proposed to stimulate the expression of virulence genes in S. aureus. Iron, which has been shown to be an important virulence determinant and required for many vital cellular processes, is not readily available for bacterial cells in the animal host. To cope with an iron-deficient host environment, the bacteria have evolved several mechanisms for iron acquisition regulation. We have cloned and characterized a ferric-uptake regulatory gene (fur) from S. aureus. This gene codes for a protein, Fur, which in the presence of sufficient intracellular iron binds to a specific DNA sequence located in the promoters of sirA and fhu and regulated their expression (Xiong et al., 2000; Cabrera et al., 2001). Our recent DNA microarray analyses indicated that many genes are differentially expressed by iron. Whether these genes are directly or indirectly under the control of Fur-iron cannot be distinguished by the microarray analysis. Therefore I propose to identify some of those genes, which are directly under the control of Fur regulation and involved in the pathogenesis of S. aureus. The long-term objective of this study is to identify Fur regulated genes, which are essential for the survival of S. aureus in the host. The specific goals of this study are: 1) to identify Fur-regulated genes with the fur mutant and the parent strains using microarray analysis followed by northern blot analysis to confirm microarray data, 2) to determine the sequences of Fur binding site of 5-10 genes which are highly regulated by Fur-iron using EMSA and DNase protection assays, and 3) to construct mutations in at least 5 genes to determine their roles in pathogenic phenotype using a mouse kidney abscess model. It is hoped that the results of these studies may find yet unidentified Fur-regulated genes involved in the iron homeostasis and pathogenesis of S. aureus. [unreadable] [unreadable]